Hi mckaskle, I own both the 740 and 760, both with drive replacements. As we in Canuckland will only be affected by the digital transition in August 2011, my knowledge on this is limited but I do understand some of the issues.
By your question I assume that you're talking about OTA (over-the-air) reception, if so, dependant on your tv's outputs (some sort of A/V outputs, I've seen tvs with audio outputs, not one with a video output yet but I would suspect some do), you'll most likely be able to record via line output of the tv to line input of the recorder, but you would be stuck watching what you're recording, similar to recording from a cable box, the NTSC tuner in the 740/760 will be useless in this manner.
If you have cable, and for a prescribed time I think, your cable provider must continue to send analog signals through the cable, then you would need to split the cable, send one to the tv and the other to the 740/760, the NTSC tuner in the recorder should be able to read the analog signals, not sure here, it is the assumption, and the tv's ATSC tuner will tune in the digital signal.
The issue with this is that eventually the cable provider will be able to switch the analog feed off. Eventually the NTSC-tuner equipped recorders will all become "tunerless" recorders hence the need to use a tuner of some sorts like a cable/satelite box/PVR. Dependant on your cable/satelite provider's boxes and systems, some do offer the ability to send one feed out and watch another, something to look into in your area for future considerations.